Rear-view mirror folding assemblies usually comprise a mirror housing or bracket, a mirror element to be attached to the mirror housing, and a mirror base to be fixedly connected to a motor vehicle, usually to the motor vehicle body.
The mirror housing is rotatably mounted on the mirror base such that it can be arranged in at least two stable positions, namely, a non-driving retracted position and a driving protracted position.
A shaft is also arranged within the mirror housing. The shaft usually has a lower end that is fixedly coupled to the mirror base and an opposite upper end that is provided with a radially protruding flange, although an inverted shaft configuration is also possible. The mirror housing can be rotated to the mirror base around said shaft. The geometric axis of the shaft will be referred herein to as mirror rotation axis. In the forthcoming, reference will be made to the usual configuration of the shaft with a lower end fixedly coupled to the mirror base and with an upper end having a radially protruding flange.
Known rear-view mirror folding assemblies are also usually provided with a metal compression spring. Such compression spring is arranged surrounding the above mentioned shaft. A lower end of the metal compression spring is arranged resting on the mirror base while an opposite upper end of the metal compression spring is arranged abutting on the above mentioned radially protruding flange of the shaft. The metal compression spring thus acts between the mirror housing and the mirror base.
A number of teeth are formed in the mirror base. Said teeth are adapted for cooperating with corresponding teeth formed in the mirror housing when in use. Both the teeth in the mirror base and the teeth in the mirror housing define inclined planes. The inclined planes, in cooperation with the compression spring, provide a mechanical resistance against an inadvertent folding of the mirror housing relative to the mirror base between said at least two stable positions, namely the above mentioned non-driving retracted and driving protracted positions. For example, during travelling of the vehicle, where the mirror housing is positioned in the driving protracted position so as to provide a vehicle driver a substantially rearward field of view, an inadvertent folding from said driving protracted position towards the non-driving retracted position could occur due to conditions such as wind, braking, inertia, door closing, etc.
When the mirror housing is rotated relative to the mirror base around the mirror rotation axis the teeth of the mirror base and the teeth of the mirror housing move to each other. During such relative movement, the respective inclined planes of said teeth cause the mirror housing to be raised or lowered relative to the mirror base depending on the direction of rotation of the mirror housing and the mirror base. Downward movement of the mirror housing relative to the mirror base as it is rotated causes the mirror housing to move towards the mirror base compressing the compression spring. In this movement of the mirror housing towards the mirror base the compression spring opposes rotation of the mirror housing for determining its relative angular positions. Upward movement of the mirror housing relative to the mirror base as it is rotated in the opposite direction causes the mirror housing to move away from the mirror base releasing the compression spring.
The use of metal compression springs has been found to involve a number of undesirable disadvantages in known rear-view mirror folding assemblies. Metal compression springs are relatively expensive to produce. They add extra weight to the whole assembly and, due to their helical configuration, assembly operations become difficult. In addition, metal compression springs generate unwanted noise in operation due to friction. Lubricant is therefore required for reducing operating noise which adds extra costs.
Solutions to the above mentioned disadvantages have been already proposed in the art. Documents EP1561642 and US2005168855 both disclose rear view mirror assemblies of the type described above. In said documents, the metal spring is replaced by a plastic hollow cylinder. Such hollow cylinder is provided with a number of openings formed in the side surface of the hollow cylinder. The openings are arranged to define helical strips. The purpose of the helical strips is to provide an elastic property in a direction that is parallel to the longitudinal axis of the above mentioned shaft that passes through the mirror housing, that is, the mirror rotation axis.
The purpose of the plastic hollow cylinder is to act against rotation of the mirror housing relative to the mirror base to define different angular positions of the mirror housing. Plastic hollow cylinders have a number of advantages over metal compression springs. The main advantage refers to cost savings and enhanced performance, especially as regards noise and lubrication.
However, it has been found that the use of a plastic hollow cylinder with openings defining strips has significant disadvantages. The manufacturing process of plastic hollow cylinders with openings defining helical strips is complex and costly, and gives rise to a reduced resistant section which results in weakening of the plastic cylinder itself. This in turn results in a significantly lower resistant capacity which disadvantageously limits the strength that the cylinder can resiliently resist.